Adding additional documentation for int-based enums

Int-based enums need an additional marshal/unmarshal functionality in order to work with GraphQL client libraries.

_examples/enum/model/model.go

@@ -1,5 +1,10 @@
 package model
 
+import (
+	"encoding/json"
+	"fmt"
+)
+
 type IntTyped int
 
 const (
@@ -12,6 +17,40 @@ const (
 	IntUntypedTwo
 )
 
+func (t IntTyped) String() string {
+	switch t {
+	case IntTypedOne:
+		return "ONE"
+	case IntTypedTwo:
+		return "TWO"
+	default:
+		return "UNKNOWN"
+	}
+}
+
+func (t IntTyped) MarshalJSON() ([]byte, error) {
+	return []byte(fmt.Sprintf(`"%s"`, t.String())), nil
+}
+
+func (t *IntTyped) UnmarshalJSON(b []byte) (err error) {
+	var s string
+
+	if err = json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+
+	switch s {
+	case "ONE":
+		*t = IntTypedOne
+	case "TWO":
+		*t = IntTypedTwo
+	default:
+		return fmt.Errorf("unexpected enum value %q", s)
+	}
+
+	return nil
+}
+
 type StringTyped string
 
 const (

docs/content/recipes/enum.md

@@ -15,6 +15,8 @@ Both typed and untyped binding are supported.
 
 More examples can be found in [_examples/enum](https://github.com/99designs/gqlgen/tree/master/_examples/enum).
 
+## Binding Targets
+
 Binding target go model enums:
 
 ```golang
@@ -80,4 +82,47 @@ models:
         value: ./model.EnumUntypedOne
       TWO:
         value: ./model.EnumUntypedTwo
-```
+```
+
+## Additional Notes for int-based Enums
+
+If you want to use the generated input structs that use int-based enums to query your GraphQL server, you need an additional step to convert the int-based enum value into a JSON string representation. Otherwise, most client libraries will send an integer value, which the server will not understand, since it is expecting the string representation (e.g. `ONE` in the above example).
+
+Therefore, we must implement `MarshalJSON` and `UnmarshalJSON` on the typed enum type to convert between both. This is only possible with typed bindings.
+
+```go
+func (t EnumTyped) String() string {
+	switch t {
+	case EnumTypedOne:
+		return "ONE"
+	case EnumTypedTwo:
+		return "TWO"
+	default:
+		return "UNKNOWN"
+	}
+}
+
+func (t EnumTyped) MarshalJSON() ([]byte, error) {
+	return []byte(fmt.Sprintf(`"%s"`, t.String())), nil
+}
+
+func (t *EnumTyped) UnmarshalJSON(b []byte) (err error) {
+	var s string
+
+	if err = json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+
+	switch s {
+	case "ONE":
+		*t = EnumTypedOne
+	case "TWO":
+		*t = EnumTypedTwo
+	default:
+		return fmt.Errorf("unexpected enum value %q", s)
+	}
+
+	return nil
+}
+```
+